The present invention relates to a method and apparatus for managing moisture buildup in humid pressurized breathing systems subject to humidity consideration, etc., e.g., breathable gas supply apparatus for use in Continuous Positive Airway Pressure (CPAP) treatment of Obstructive Sleep Apnea (OSA) and various other respiratory disorders, and diseases. In one example, a respiratory mask is provided with a vent affording reduced noise and/or improved vent flow under humidified gas flow conditions.
CPAP treatment devices typically provide a gas flow generator for delivering pressurized breathable gas, usually air, to a patient's airway using a conduit and mask. In many such devices, the gas flow generator is combined with a humidifier to deliver pressurized humidified gas. The pressurized and optionally humidified gas acts as a pneumatic splint for the patient's airway, preventing airway collapse, especially during the inspiratory phase of respiration. The humidified gas minimizes drying of the nasal mucosa and increases patient comfort. Many standard vents for respiratory masks have adverse reduced flow when used with humidified air, either due to the build up of moisture at the entry to the vent or the blocking of the small gas pathways through the vent. For example, the vent manufactured by Gottlieb Weinmann Gerate Fur Medizin Und Arbeitsschutz GmbH & Co. is known to reduce the vent flow when used with humidified gas. See European Patent No. 0 697 225 A2 to Gottlieb et al. The blockage of the small gas pathways through the vent is a particular problem at low pressures such as 4 cm of H2O or below. Blockage may occur because pressure is insufficient to keep the pathways clear. In this event, the minimum flow condition for safe CO2 washout may be compromised, especially at the low end of the pressure treatment range.
Further, standard vents, including low noise vents, sometimes encounter obstruction of the gas vent pathway following washing of the mask or vent. Moisture can be retained around the entry or the exit of the vent or within the internal pathways of the vent. At low pressures immediately following a washing of the mask or vent, considerable time may elapse before the moisture is cleared. If the mask is in use while the vent is being cleared, the system has reduced airflow leading to undesirable retention of CO2 within the mask.